In a conventional electrical connection unit of this type, a connector cavity is formed on a lower portion of the junction box, on which are mounted electrical parts such as relays and/or fuses. A connector from which a wire harness is extended is directly assembled and inserted into the connector cavity. In the unit, a nut is fixed to the junction block and a bolt opening is formed on the connector. A fastening bolt is passed through the bolt opening from below the connector and is screwed to the nut, thus tightening and fixing the junction block and the connector to each other. In this assembled state, the wire harness is extended in a restricted manner in a prescribed direction.
Alternatively, the junction block can be connected to the connector by having it mounted inside the unit and having the connector installed therein. In these units, the connection of the junction block and the connector requires proper centering at prescribed positions of the junction block and the connector relative to each other. Thus, a centering adjuster containing a spring is disposed on the connector cavity of the junction block or the main unit. The pressure from this spring centers the connector when the connector is connected to the junction block. However, the use of the centering spring to properly locate the junction block and the connector results in a complex structure and increased production costs.